Two site conditions, geothermal temperature and geothermal heat flow, are required to generate electricity using geothermal heat, which is a new and renewable energy. The higher the geothermal temperature and the more the geothermal heat flow, the larger and the more economical geothermal power generation is possible. The geothermal temperature is a condition that cannot be artificially produced, but is naturally generated, and is a necessary condition for geothermal power generation.
In general, the deeper under the ground, the higher the temperature due to the heat of the mantle under the crustal. This increasing rate is called a geothermal gradient (° C./km). It is possible to measure the geothermal temperature (ground temperature) of deep parts using the geothermal gradient. The geothermal gradient can be obtained from the following equation:geothermal temperature=geothermal gradient×depth+earth surface temperature.
Geothermal heat flow calculated from a geothermal gradient and heat conductivity measured at a specific point is representative geothermal heat flow of the corresponding area, but there is a problem with how the geothermal heat flow is reliable as the representative value at the point.
In general, the geothermal temperatures for each depth measured through an exploratory hole have changes at each depth, but the geothermal gradient values may be understood as geothermal temperatures approximated to values that simply increase at each depth. Furthermore, when several geothermal gradient values are shown in a narrow area, a representative value was simplified to an average value regardless of degree of quality of the geothermal gradient values. Furthermore, the depth of measuring geothermal temperature through an exploratory hole is within hundreds of meters, so the reliability of geothermal gradient values of deep parts is not high. It is required to bore a hole to several kilometers in order to estimate an exact geothermal gradient value, but the expensive is high in this case.
Furthermore, it is possible to estimate the geothermal temperature of a point where geothermal temperature was not measured, using geothermal temperatures measured at various points, but meaningful estimation may be impossible when the spatial density of the measured values is low or is not uniform.
In the geothermal resource distribution map that is generally used now for power generation from deep parts in Korea, data measured at 352 biased points (spa zones over 70%) are spatially smoothened (Non-Patent Document, Estimation of Theoretical and Technical Potentials of Geothermal Power Generation using Enhanced Geothermal System, Economy and Environment Geology, V. 44, N. 6, 513-523, 2011, Yoonho Song et al.) However, in this spatial smoothing, the crustal characteristics relating to the geothermal characteristics of deep parts are never considered, so it is meaningless to estimate geothermal heat through spatial smoothing that uses arbitrary parameters with geothermal measurement data biased to spa zones.
In order to overcome the limit in this geothermal estimation method, geothermal heat flow in Korean has been estimated by selecting the kinds of rocks, the generation age of geological stratums, and the depth of the Moho plane as earth science information relating to geothermal heat flow, by classifying the information in specific ranges, by calculating the average geothermal heat flow in each of the ranges, and by using the following geothermal heat flow equation Qs (Interpretation of geothermal anomaly using heat flow and geological data in South Korea, p. 80-86 doctoral dissertation, applied geology, geology department, graduate course, ChungNam Univ., 2004, 2, KIM, Hyung Chan).Qs=average of geothermal heat flow for each kind of rock+average of geothermal heat flow for each geological age+average of geothermal heat flow for each depth of Moho plane
However, the geothermal heat flow distribution estimated by this method shows zoning in which the values are all the same in a specific zone and there is no quantitative data that prove the relationship between the estimated result and the actually measured geothermal heat flow.
(Non-Patent Document 1) Non-Patent Document 1: Estimation of Theoretical and Technical Potentials of Geothermal Power Generation using Enhanced Geothermal System, Economy and Environment Geology, 44th Vol., 6 issue, 513-523, 2011, Yoonho Song et al.
(Non-Patent Document 2) Non-Patent Document 2: Interpretation of geothermal anomaly using heat flow and geological data in South Korea, p. 80-86 doctoral dissertation, applied geology, geology department, graduate course, ChungNam Univ., 2004, 2, KIM, Hyung Chan